1. Field of the Invention
This invention relates generally to drive rollers and drilling mud separation units, and more particularly to cylindrical composite rollers having a thick elastomeric outer layer for use in an endless-belt drilling mud separation unit, and a drive roller having a plurality axially spaced circumferential rows of radially extending elastomeric teeth that receive and engage the openings in a wide belt formed of a plurality of laterally adjacent hinged links to drive the belt and reduce wear, prevent sparking, and dislodge materials which may otherwise clog the belt openings.
2. Brief Description of the Prior Art
Effective solids control systems for controlling the solids in drilling mud have been a goal in the oilfield industry for many years. Various systems have been employed to give higher penetration rates, less contamination of formations, lower mud costs, and less abrasive and sticky materials in the mud system. The systems which are most effective require expensive and complicated machinery and require personnel to monitor and maintain the machinery. Common apparatus used for mechanically removing solids from drilling mud include shale shakers and vibratory screens, desanders, desilters, mud cleaners, and centrifuges. Each piece of equipment is limited to a range of various particle sizes and selectively rejects undesirable solids and retains desirable solids in the drilling fluid.
The shale shakers and mud cleaners employ a vibrating screen to selectively classify particles by size differences. The desander, desilter, and centrifuge are usually located downstream from the shale shaker and utilize centrifugal force and mass difference between the solids density and liquid density for solids removal.
The initial removal step in most solids control systems is to conduct the drilling mud from the well directly to a shale shaker. Vibrating screen shale shakers of the type used in the oil industry fall into three general categories, as described below.
"Elliptical motion," or "unbalanced design" shakers have a downward slope on the screen to transport cutting across the screen and off the discharge end. Optimum screening with these types of shakers is usually in the range of 30-40 mesh (400-600 microns), and they are prone to bearing failure.
"Circular motion," or "balanced design" shakers produce a balanced, or generally circular motion. The consistent, circular vibration allows solids transport with the basket in a flat, horizontal orientation. This type of shaker usually has multiple decks to split the solids load and allows the use of finer mesh screens in the range of 80-100 mesh (150-180 microns).
"Linear motion," or "straight-line motion" shakers produce a generally straight motion. This motion is developed by a pair of eccentric shafts rotating in opposite directions. Linear motion shakers provide superior cutting conveyance and are able to operate at an uphill slope which allows the use of 200 mesh screens (77 microns).
Most prior art shakers tend to force the cuttings upward from the screen surface and as they continue upward the screen travels down, and as the cuttings fall downward, the screen travels upward and strikes the cuttings which chips small pieces off and creates very fine cuttings that are extremely difficult to remove. Shale shakers are prone to short screen life and their vibratory action tends to drive the cuttings into the screen and leads to screen "blinding" resulting in loss of fluid across the screen. "Blinding" is known as the phenomenon where near-size particles plug the screen or the screen becomes coated with sticky particles.
Lee, U.S. Pat. No. 4,146,483 discloses a segmented endless belt vibrating screen for removing solid particles from a stream of drilling fluid circulated therethrough. The screen assembly is formed of laterally spaced segments of one or more layers of open mesh screens interconnected by longitudinal rubber support belts disposed therebetween and a pair of rubber strips along the outermost lateral side edges. The rubber strips along the outermost lateral side edges are connected by L-shaped hooks to a pair of rubber V-belts which are received in V-shaped rollers with one set of rollers driven by a motor. The mesh screens are cleaned by a set of nozzles which direct a spray of water onto the screen at a point prior to it passing over a rubber wiper.
Hamacheck III, U.S. Pat. No. 3,631,980 discloses an open mesh belt cleaner for cleaning the bight openings of a link screen conveyer belt in a pea-harvesting machine. The endless belt link screen is supported and driven by a sprocket at each lateral side of the belt which have teeth that engage the links of the belt. The belt cleaner comprises one or more bars which extend transversely between the sprockets and each bar replaces one of the teeth of the opposed sprockets. The bar is provided with a series of debris expelling metal teeth along its length in staggered registry with certain ones of the openings in the belt to penetrate the openings of different rows in successive passes of the belt. Hamacheck III states that it would be undesirable to employ the metal teeth to clean all the successive rows of belt openings in every pass of the belt.
The present invention is distinguished over the prior art in general and these patents in particular by a pair of cylindrical composite rollers formed of a metallic drum with a thick outer elastomeric layer that are mounted transversely in a rectangular frame of a drilling mud separation unit over which a wide endless-loop chain-link belt is driven in a continuous loop moving along the longitudinal axis of the frame. The drive roller has a plurality of axially spaced circumferential rows of radially extending teeth that are machined in the surface of the elastomeric material. The endless belt is formed of a plurality of laterally adjacent jointed links hinged together by transverse rods. As drilling mud or drilling fluids are conducted onto the moving belt, liquids and particles smaller than the openings in the belt pass through the openings and liquids and particles larger than the openings are transported on the moving belt and are discharged off of one end as the belt completes its path. The teeth of the drive roller are sized and spaced to receive and engage the plurality of laterally adjacent jointed links of the wide belt and are of sufficient length to protrude slightly beyond the outer surface of the links as they pass around the front drive roller to dislodge gumbo and other large solids which may otherwise stick in the openings of the links and clog the belt. The elastomeric roller surfaces and teeth reduce wear and prevent metal-to-metal contact and sparking.